1. Field of the Invention
The present invention relates to a vertically oriented liquid crystal display element.
2. Brief Description of the Related Art
FIGS. 11A and 11B are drawings illustrating an arrangement of a typical vertically oriented liquid crystal display element (hereinafter referred as xe2x80x9cLCD elementxe2x80x9d). FIG. 11A is a side view and FIG. 11B is a plan view.
Reference characters xe2x80x9c101axe2x80x9d and xe2x80x9c101bxe2x80x9d in FIG. 11A are an upper glass substrate and a lower glass substrate and liquid crystal molecules 102 are sandwiched in between. On inner surfaces of both glass substrates, transparent electrodes (not shown in FIG. 11A) for driving liquid crystal molecules are formed. Reference characters xe2x80x9c103axe2x80x9d and xe2x80x9c103bxe2x80x9d are polarizing plates and a reference character xe2x80x9c104xe2x80x9d is a visual angle compensation film. In FIG. 11B, a reference character xe2x80x9cXxe2x80x9d is a light transmission axis of the upper polarizing plate 103a, a reference character xe2x80x9cYxe2x80x9d is a light transmission axis of the lower polarizing plate 103b and reference character xe2x80x9cZxe2x80x9d is a tilting direction of the liquid crystal molecules 102.
In the LCD element, a liquid crystal cell consisting of the vertically oriented liquid crystal molecules, is arranged between the polarizing plates 103a and 103b arranged in a cross Nicol relation each other such that the tilting direction Z and the light transmission axis X of the polarizing plate 103a form an angle of 45 degree, and the tilting direction Z and the light transmission axis Y of the polarizing plate 103b also form an angle of 45 degree. The tilting direction Z of the liquid crystal molecules is controlled by a pre-tilted angle, which is attained when vertically orienting membranes (not shown in FIG. 11A) applied and baked on the glass substrates are treated, for example, are rubbed in a predetermined direction. In addition, a visual angle compensation film 104 is inserted between the upper glass substrate 101a and the upper polarizing plate 103a In order to improve obliquely viewed visibility of the LCD element.
A uniaxial optical film having-an optical axis normal to a film plane and having a negative double refractive index [=(a refractive index in the film plane)xe2x88x92(a refractive index in the optical axis)] is employed as the visual angle compensation film 104. The visual angle compensation film 104 can be arranged at one side or both sides of the liquid crystal cell. A suitable retardation value of the visual angle compensation film 104 is approximately in a range from one third to the same retardation value of the liquid crystal cell. xe2x80x9cRetardation valuexe2x80x9d is an index defined as follows: (a difference between a refractive index on the film plane and a refractive index in a normal direction to the film plane)xc3x97(a thickness of the film). If the visual angle compensation films 104 are arranged on both sides of the liquid crystal cell, a combined retardation value xe2x80x9cwith retardation values of both films should be adjusted in the above-mentioned range.
The above-mentioned LCD element is proposed by the same inventors as inventors of the present invention.
Another LCD element, for example, Japanese patent registered No. 3108768 proposes an electrode arrangement where transparent electrodes on the upper and lower glass substrates are partially removed, so as to form slits in the electrodes. And the slits on the upper and lower electrodes are alternately arranged when the electrodes are vertically viewed. Other LCD element, for example, Japanese patent registered No. 3324926 proposes another electrode arrangement where elongated slits are respectively formed in pairs on an upper substrate and a lower substrate.
Since liquid crystal molecules in the above-mentioned LCD elements are tilted in one direction, obliquely viewed visibility of these LCD elements is not improved as shown in FIG. 12 even when visual angle compensation films are combined.
In FIG. 12, digits around a most outer circle are viewing directions projected on a horizontal plane. Namely, xe2x80x9c0xe2x80x9d means, a viewing direction from the right side and xe2x80x9c180xe2x80x9d means a viewing direction from the left side. Concentric circles (0 to 60) are angles formed between the viewing directions and a normal line to the LCD element, namely, xe2x80x9c0xe2x80x9d means a viewing direction normal to the LCD element and xe2x80x9c60xe2x80x9d means a viewing direction having an angle of 60 degree against the normal line. A reference character xe2x80x9cCRxe2x80x9d in the drawing means a ratio of a bright transmission rate/a dark transmission rate (a contrast value) in respective viewing directions. Which means the larger a CR value is, the clearer a displayed image in the LCD element is.
FIG. 12 indicates the obliquely viewed visibility of the above-mentioned LCD element In a tilting direction of the liquid crystal molecules (in this case in a 6 o""clock direction) is deteriorated such that contrast values In some area are less than 1, in other words, inverted contrast areas are formed (hatched areas in FIG. 12).
The present invention is carried out in view of the above-mentioned problems in order to provide a vertically oriented LCD element of higher quality by improving obliquely viewed visibility so as to obtain almost uniform visibility viewed from any direction.
The following arrangements by the present invention can provide the LCD element mentioned above.
(1) A liquid crystal display element comprising: a pair of substrates; transparent electrodes having predetermined patterns formed on the respective substrates; vertical orienting membranes respectively formed on the transparent electrodes; and a liquid crystal layer consisting of the liquid crystal molecules sandwiched by the substrates, wherein: pair of the substrates are arranged such that: respective transparent electrodes face each other; series of the nearly rectangular slits are formed on respective transparent electrodes by removing portions of the electrodes in a display area formed by the electrodes; and series of the slits on one and other transparent electrodes are alternately arranged in a normal direction to a longitudinal direction of series of the slits, when the substrates are viewed vertically.
(2) The liquid crystal display element according to (1), wherein: a width of the slits in the normal direction to the longitudinal direction of the slits is set more than 10 xcexcm, but less than 30 xcexcm.
(3) The liquid crystal display element according to (1), wherein: a width of the slits in the normal direction to the longitudinal direction of the slits is set 2.5 times more than a thickness of the liquid crystal layer.
(4) The liquid crystal display element according to (1), wherein: a horizontal distance between two neighboring alternately arranged slits in the normal direction to the longitudinal direction of the slits is set more than 10 xcexcm, but less than 60 xcexcm.
(5) The liquid crystal display element according to (1), wherein: a horizontal distance between two neighboring alternately arranged slits in the normal direction to the longitudinal direction of the slits is set more than the width of the slits, but less than 60 xcexcm.
(6) The liquid crystal display element according to one of (1) to (5), wherein: the display area is a segment display type area.
(7) The liquid crystal display element according to one of (1) to (5), wherein: the display area is a dot-matrix display type area driven by a simple matrix driving method.
(8) The liquid crystal display element according to one of (1) to (5), wherein: the display area is a area combined a segment display type area and a dot-matrix display type area driven by a simple matrix driving method.
(9) The liquid crystal display element according to one of (1) to (5), wherein: the display area is a dot-matrix display type area driven by an active matrix.
(10) The liquid crystal display element according to (7) or (8), wherein: slits both ends of one dot in a normal direction to the longitudinal direction of the slits are formed on the electrode arranged normal to the longitudinal direction of the slits.
(11) The liquid crystal display element according to (9), wherein: outermost slits in the normal direction to the longitudinal direction of the slits are formed on a common electrode facing a certain pixel electrode.
(12) The liquid crystal display element according to (1), wherein: the slit is divided into a plurality slits In the longitudinal direction of the slit.